CODEWITHSUNDEEP
pythondjangodjango-rest-framework
Robert Kajic
Robert Kajic

Reputation: 9087

Add user specific fields to Django REST Framework serializer

I want to add a field to a serializer that contains information specific to the user making the current request (I don't want to create a separate endpoint for this). Here is the way I did it:

The viewset:

class ArticleViewSet(viewsets.ModelViewSet):
    queryset = Article.objects.all()
    serializer_class = ArticleSerializer
    filter_class = ArticleFilterSet

    def prefetch_likes(self, ids):
        self.current_user_likes = dict([(like.article_id, like.pk) for like in Like.objects.filter(user=self.request.user, article_id__in=ids)])

    def get_object(self, queryset=None):
        article = super(ArticleViewSet, self).get_object(queryset)
        self.prefetch_likes([article.pk])
        return article

    def paginate_queryset(self, queryset, page_size=None):
        page = super(ArticleViewSet, self).paginate_queryset(queryset, page_size)
        if page is None:
            return None

        ids = [article.pk for article in page.object_list]
        self.prefetch_likes(ids)

        return page

The serializer:

class ArticleSerializer(serializers.ModelSerializer):
    class Meta:
        model = Article

    def to_native(self, obj):
        ret = super(ArticleSerializer, self).to_native(obj)

        if obj:
            view = self.context['view']
            ret['has_liked'] = False
            if hasattr(view, 'current_user_liked'):
                ret['has_liked'] = obj.pk in view.current_user_liked

        return ret

Is there a better place to inject the prefetching of liked articles, or a nicer way to do this in general?

Upvotes: 13

Views: 10088

Answers (3)

Tobias Ernst
Tobias Ernst

Reputation: 4654

According to the Django Documentation - SerializerMethodField, I had to change the code of rapid2share slightly.

class ResourceSerializer(serializers.ModelSerializer):
    liked_by_user = serializers.SerializerMethodField()

    def get_liked_by_user(self, obj : Resource):
        request = self.context.get('request')
        return request is not None and obj.likes.filter(user=request.user).exists()

Upvotes: 1

rapid2share
rapid2share

Reputation: 542

you can do it with SerializerMethodField

Example : 

class PostSerializer(serializers.ModelSerializer):
    fav = serializers.SerializerMethodField('likedByUser')

    def likedByUser(self, obj):
        request = self.context.get('request', None)
        if request is not None:
            try:
                liked=Favorite.objects.filter(user=request.user, post=obj.id).count()
                return liked == 1
            except Favorite.DoesNotExist:
                return False
        return "error"

    class Meta:
        model = Post

then you should call serializer from view like this:

class PostView(APIVIEW):
     def get(self,request):
         serializers = PostSerializer(PostObjects,context={'request':request})

Upvotes: 27

Carlton Gibson
Carlton Gibson

Reputation: 7386

I'd be inclined to try and put as much of this as possible on the Like model object and then bung the rest in a custom serializer field.

In serializer fields you can access the request via the context parameter that they inherit from their parent serializer.

So you might do something like this: 

class LikedByUserField(Field):
    def to_native(self, article):
        request = self.context.get('request', None)
        return Like.user_likes_article(request.user, article)

The user_likes_article class method could then encapsulate your prefetching (and caching) logic.

I hope that helps.

Upvotes: 8

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